Process for purifying acrylonitrile



Nov. 7, 1961 G. PATRON ETAL 3,007,853

PROCESS FOR PURIFYING ACRYLONITRILE Filed Dec. 10., 1958 1N VENTORS GERM/4 N0 PA TON MA 56/M0 SCA T'VA ATTORNEYS rates atet 3,007,853 Patented Nov. ll

3,007,853 PROCESS FOR PURIFYIWG ACRYLONITRILE Germano Patron and Massimo Scatena, Milan, Italy, assignors to Sicedison SpA., Milan, Italy Filed Dec. 10, 1958, Ser. No. 779,372 Claims priority, application Italy Dec. 24, 1957 7 Claims. (Cl. 202-57) This invention relates to a new process for purifying acrylonitrile from usually associated impurities, particularly methylvinylketone.

yIt is known that acrylonitrile is produced by a synthesis from acetylene and hydrogen cyanide in the presence of a catalyst based on cuprous salts. The resulting crude reaction `product is subsequently purified by proper absorption and distillation steps.

In this marmer, a product is obtained which is commercially suitable -for a variety of purposes. However, certain impurities always contained in the synthetically produced acrylonitrile make the latter unsuited for use in certain types of polymerizations. Particularly deterimental among these impurities are secondary reaction products of acetylene, such as monovinylacetylene and div-inylacetylene, or condensation products between acetylene derivatives and hydrogen cyanide, such as, for instance, the l-cyanobutane-Z-i-diene, or products of the condensation -between acetylene derivatives and Water, such as methylvinylketone. A reaction mechanism leading to the formation of methylvinylketone is, for nstance, represented by the following equation:

Cuprous salts E GH2=CH-CECH Monovinylacetylene Methylvinylketone could also be formed during the synthesis of acrylonitrile by a reaction between acetylene and intermediarily lformed acetaldehyde.

While the most of the above-mentioned products which result detrimental for the use of acrylonitrile in particular types of polymerization may be removed relatively easily by means of repeated distillations of acrylonitrile, the methylvinylketone cannot be eliminated practically in this manner, as the boiling points of methylvinylketone and acrylonitrile are very close to each other, namely at about 80.0 C. `and 77.3 C., respectively.

The separation by distillation of this undesirable impurity would result excessively diicult and expensive. For it would be necessary to use very efcient fractionating columns with high rellux rates, since the degree of purity, which must be attained with respect to the methylvinylketone, is extremely high, i.e. less than 100 ppm. for every part of acrylonitrile; consequently there would arise the danger of a. premature polymerization of still impure acrylonitrile.

It is, therefore, the object of our present invention to overcome the afore-described dilliculties by providing a suitable process for the purication of acrylonitrile from the impurities usually accompanying the former.

It is more particularly the object of our invention to provide a process adapted for satisfactorily separating acrylonitrile from methylvinylketone.

It is nally an object of our invention to reduce the content of methylvinylketone in acrylonitrile to less than 100 ppm.

These objects are attained by the process of purifying acrylonitr-ile from methylvinylketone and similar impurities by adding to the crude reaction product of the synthetic production of acrylonitrile small amounts of anhydrous aluminum trichlon'de, whereby complexes of the latter with methylvinylketone are formed, which complexes are stable when heated and have a much higher boiling point than the acrylonitrile and ordinary methylvinylketone. It thus becomes possible to remove these complexes easily and completely by fractionated distillation in non-critical temperature ranges from the acrylonitrile to be purified.

The reaction may be carried out by dissolving in acrylonitrile a small amount of anhydrous aluminum chloride at room temperature, in proportion with the quantity of methylvinylketone present. As .an order of magnitude, in practical operation, it is suflcient t0 add aluminum chloride iu about a concentration of Q01-5% by Weight of the acrylonitrile. Formation of the complex should take place with the lowest possible water content, preferably not exceeding 0.5 part by weight of water for parts of aerylonitrile (0.5%). While good results have been obtained with products containing water at 0.15% by weight, it is evident that in this case a greater amount of aluminum chloride is consumed, than if the water content is kept still lower. Moreover larger amounts of water would lead to the yformation of considerable amounts of aluminum hydrate, the presence of which could be inconvenient. Excellent results were obtained when the Water content in acrylonitrile was held between (LGS-0.08% by weight.

Since the reaction takes place almost instantaneously the Contact time of the reactant with acrylonitrile need not be 'long and the distillation can then be carried out immediately following the treatment with anhydrous aluminum chloride. In order to avoid undesirable polymerizations during the distillation it is preferable to operate in the presence of stabilizers on a copper basis, such as cuprous chloride. The distilled product is acidic due to the presence therein of hydrochloric acid; this acidi-ty is undersirable and must, therefore, be removed either by neutralization with an organic or inorganic base, or by using ion-exchange resins.

Suitable ion-exchange resins are, for instance, Amberlite type resins, manufactured by Rohm & Haas Co., Philadelphia, U.S.A.

In order to better understand the invention the following examples are given -by way of illustration and are not to be intended to limit the invention.

Example I 0.4 g. anhydrous aluminum chloride are added to 200 g. acrylonitrile containing rabout 700 ppm. methylvinylketone and 0.02% water at room temperature. After aluminum chloride is completely dissolved, the mixture is distilled in the presence of about 20 ppm. cuprous chloride as inhibitor at a temperature of 77.3 C. at the top of the distillation column. The distilled product, which represents a yield of 97-98% of the star-ting mixture, was neutralized with aqueous NaOH (sodium hydroxide) solution at room temperature. The formed complex Ibetween aluminum chloride and methylvinylketone remains in the residue. The thus treated acrylonitrile is analyzed and the analysis shows that methylvinyl-ketone is present in a quantity lower than 15 p.p.m.

Example la Example Il 0.4 g. anhydrous aluminum chloride are added to 200 g. acrylonitrile containing about 700' ppm. methylvinylketone `and 0.02% water at room` temperature. After the aluminum chloride is completely dissolved, the mixture is distilled at 77.3 C., at the top of the distillation column, in the presence of 20 p.p.m. cuprous chloride as inhibitor. The product which represents 97 to 98% of the starting mixture is neutralized with diethylamne. The analysis of the thus treated acrylonitrile shows an amount of less than 15 ppm. methylvinylketone.

Example Ill 0.4 g. anhydrous aluminum chloride are added to 200 g. acrylonitrile containing about 700 ppm. methylvinylketone and 0.02% water at room temperature. After the aluminum chloride was completely dissolved, the mixture is distilled at about 80 C. in the presence of cuprous chloride as inhibitor. The product which repre sents 97-98% of the starting mixture is passed over a bed of ion-exchange resin of anionic type, for instance, Amberlite manufactured by Rohm & Haas Co., Philadelphia, U.S.A.

Analysis of the purified acrylonitrile shows an amount of less than l ppm. methylvinylketone.

Example IV 200 gr. per hour of acrylonitrile containing 0.07% w-ater and 700 ppm. methylvinylketone, and 8 gr. per hour of a solution of 5% by Weight of anhydrous aluminum chloride in acrylonitrile, are separately poured, by continuous addition, into a ask provided with a stirrer. The flask contains, at the start, 200 gr. of the aforesaid acrylonitrile and 8 gr. of the aforesaid anhydrous aluminum chloride-acrylonitrile solution.

The ilask mixture is stirred, at room temperature, at

about 150 rpm. and continuously transferred into av second flask at the rate of about 210 gr. per hour. From the latter ilask the mixture is distilled at 77.3 C. and collected -at a rate of about 200 gr. per hour. The second flask is charged with 20 p.p.m. of cuprous chloride as polymerisation inhibitor.

Operation of the apparatus for 40 hours yields a total of about 8000- grams of acrylonitrile. Samples taken every 2 hours are analyzed after neutralization, for instance, with NaOH, and reveal a methylvinylketone content which is each time below 15 ppm.

The process can also be carried out in a continuous manner as illustrated in the accompanying flow sheet. Crude acrylonitrile produced by catalytic synthesis and containing the described impurities is passed in a continuous llow through the reactor, provided with a stirrer, also acrylonitrile-anhydrous aluminum chloride solution is continuously added to said reactor. The methylvinylketone content in the acrylonitrile is converted to the high boiling complexes with A1Cl3 described above,

which pass with the acrylonitrile into the distilling column. In this column distillation may be carried out at 77.3 C. and atmospheric pressure, or at -a pressure of 200 Torr. (mm. of Hg) and about 40 C.

A polymerization inhibitor is present during the distillation. The distillate is then neutralized by adding basic substance, and pure acrylonitrile can be obtained by further distillation.

The residue from the distilling column containing the aluminum chloride complexes and small amounts of acrylonitrile can be reworked for acrylonitrile recovery. The said residue can rst be separately distilled on a distillation column, and then be treated again in a reactor with anhydrous aluminum chloride as described above.

It will be understood that this invention is susceptible to further modication and, accordingly, it is desired to comprehend such rnodcations within this invention as may fall within the scope of the appended claims.

What is claimed is:

1. A process for the purification of crude acrylonitrile having impurities comprising methylvinyl ketone, as an impurity, said process comprising the steps of: mixing aluminum chloride with said crude acrylonitrile; reacting said aluminum chloride with said impurity to form high boiling compounds; and then distilling the acrylonitrile from said high boiling compounds.

2. The process described in claim l wherein the crude acrylonitrile contains up to 5% by weight of water.

3. The process described in claim 1 wherein the crude acrylonitrile contains from CD3-0.08% by weight of water.

, 4. .The process described in claim l wherein the distillation is accomplished in the presence of a stabilizer in order to prevent polymerization of the acrylonitrile.

5. The process described in claim 1 wherein the amount of aluminum chloride added to the crude acrylonitrile amounts to about 0.01% to about 5% by weight of the latter.

6. The process described in claim 1 wherein the crude acrylonitrile contains up to 5% by weight of water and the amounts of aluminum chloride added to the acrylonitrile amounts to 0.01% to about 5% by weight of the latter.

7. A process for the purication of crude acrylonitrile having methylvinyl ketone as an impurity, said process comprising the steps of: mixing aluminum chloride with said crude acrylonitrile; reaching said aluminum chloride with said impurity to form high boiling compounds; distilling the acrylonitrile from said high boiling compounds; adding suicient alkaline reagent to said distilled acrylonitrile to neutralize any residual acidity; and then redistilling said acrylonitrile to obtain a pure anhydrous product.

References Cited in the file of this patent UNITED STATES PATENTS 2,000,881 Coleman May 7, 1935 2,126,277 Pickett Aug. 9, 1938 2,228,366 Rumscheidt et al. Jan. 14, 1941 2,296,218 Middleton Sept, 15, 1942 2,382,383 Carpenter Aug. 14, 1945 2,455,159 Bremmer et al Nov. 30, 1948 2,656,376 Martino Oct. 20, 1953 2,739,930 Borrel et a1 Mar. 27, 1956 2,770,644 Owens Nov. 13, 1956 2,784,216 McDonald Mar. 5, 1957 2,792,415 Higgins May 14, 1957 

1. A PROCESS FOR THE PURIFICATION OF CRUDE ACRYLONITRILE HAVING IMPURITIES COMPRISING METHYLVINYL KETONE, AS AN IMPURITY, SAID PROCESS COMPRISING THE STEPS OF: MIXING ALUMINUM CHLORIDE WITH SAID CRUDE ACRYLONITRILE, REACTING SAID ALUMINUM CHLORIDE WITH SAID IMPURITY TO FORM HIGH 